There are situations where it is advantageous to be able to direct a beam of light to a specific point in space accurately, repeatably and quickly.
The simplest approach is to mount a mirror on some mechanical orientation device, e.g. a gimbal mount, which aims the beam to the desired point. In this method, however, a 1 degree error in the orientation of the mirror leads to a 2 degree error in the direction of the beam. This method is also characterized by slow response time, and complex mechanical construction.
A second approach is to fabricate holographic diffraction gratings on a flat glass substrate. In this method the direction of the beam is determined by the orientation of the beam with respect to the grating. Typically a number of gratings are fabricated around a common axis on a single substrate. The orientation of the beam with respect to the gratings is achieved by rotating the substrate about the axis. In this method a 1 degree error in rotation of the grating results in a .sqroot.2 degree error in the direction of the beam. This is only a 29% improvement in error sensitivity.
The present invention employs a flat glass substrate onto which a number of optical elements have been fabricated. These optical elements are segments of Fresnel zone plates. These lenses have a common optical axis but are angularly displaced from each other about the common axis. As the glass substrate is rotated about the axis, an input beam of light would be incident on different Fresnel lenses, and thus be focused to some point in space. As long as the input beam of light is incident on a single Fresnel lens element it will be directed to a single point in space. In this way the direction of the beam of light is insensitive to errors in positioning within a lens element, and as a result the desired accuracy and repeatability are achieved.